In the context of the present invention:                the expressing “taxiing on the ground” should be understood to mean any possible type of taxiing of an aircraft, such as taxiing on a runway during landing and take-off phases, or taxiing on taxiways or on maneuvering areas, in particular;        the expression “convoy of aircraft” should be understood to mean a coherent set of at least two aircraft following one another in Indian file This set is coherent if the members of the convoy are likely to exchange, between them and with ground control, information making it possible to follow a trajectory on the ground according to a behavior (particularly in terms of speed and/or acceleration) suited to the stability and the safety of the convoy;        the expression “automation” should be understood to mean the action of a device capable of handling, partially or totally, that is, without assistance or with partial human assistance, the control of an aircraft on the ground; and        the expression “control” should be understood to mean the action of directing the maneuvers, or movements, of the aircraft on the ground.        
Currently, the pilot controls the movements of the aircraft on the ground, using manual piloting members (for example a control wheel used to steer the wheel of the front landing gear, an engine thrust control lever, brake pedals, a rudder bar), along a trajectory on the ground. These members are used to control actuators of the aircraft capable of influencing the movements of the aircraft, in particular through the intermediary of the engines, the brakes, the orientation of the wheel of the front landing gear (and possibly the orientation of the rear gears), and the drift control rudder.
The term “trajectory on the ground” designates the path taken by the aircraft on an airport area such as an aerodrome or an airport, including in particular the take-off and landing runways, the taxiways, the turn-around areas, the holding bays, the stop bars, the stands, the maneuvering areas and the parking areas.
The trajectory on the ground is generally supplied to the pilot, in particular via radiocommunication means or another usual means such as a digital data transmission link, by an air traffic controller or by a ground controller, but it can also, in certain cases, be chosen freely by the pilot.
The trajectory is defined in the form of a succession of elements
of the airport area, and it indicates a path making it possible to reach, from a point or region of the airport area, another point or region of this area.
The expression “element of the airport area” denotes any portion of the area, designated or not by a name, and identified as a distinct and delimited part of the area. An element can, if necessary, include one or more others. The term “element” designates in particular the take-off and landing runways, the taxiways, the turn-around areas, the holding bays, the stop bars, the stands, the maneuvering areas and the parking areas.
Knowing the ground trajectory to be followed, the pilot acts on the abovementioned piloting members, in order to the control the movements of the aircraft on the ground (the longitudinal speed and the lateral displacements of the aircraft). He also does so to follow the trajectory so that all parts of the aircraft in contact with the ground (the wheels of the front and rear landing gears) remain permanently on the surface provided for aircraft taxiing. For most airports accommodating civilian or military transport airplanes, the term “ground” is understood to mean the parts covered with tarmac and provided for this purpose. The objective of the pilot is therefore to manage a trajectory so that none of the parts of the aircraft in contact with the ground is, at a given moment, on a portion of the airport area not designed for aircraft taxiing, in particular portions covered with grass, earth or sand, or portions designed solely for the taxiing of lighter vehicles (cars, trucks).
During this taxiing phase, the pilot may be required, on instruction or not from ground control, to follow at a given distance another aircraft taxiing on the ground, which can be likened to an informal and non-coherent convoy of two aircraft. This is generally the case when they are both following one and the same trajectory portion, or they are going to places close to the airport.
The manual piloting of an aircraft on the ground represents a major workload for the pilot. The latter must in practice:                follow the trajectory provided, controlling both the speed of the aircraft with the engine thrust levers and the brake pedals, and the rotation along the yaw axis with the control wheel and rudder bar;        be careful not to depart from the surface provided for aircraft taxiing; and        monitor the external environment, in particular;                    the movements of the other vehicles maneuvering in the airport area, in particular the aircraft currently taxiing on the ground, taking off or landing, cars and trucks; and            the obstacles present around the aircraft and likely to cause a close contact with the latter, in particular the buildings, the passenger bridges, the antennas, the indication and signaling panels, and the other vehicles on the ground, whether immobile or not (aircraft, cars, trucks, apron drive passenger bridges).                        
This major workload can, consequently, affect the vigilance of the pilot, and lead, in particular, to an unscheduled trajectory being followed, departures from the surface provided for aircraft taxiing, and close contacts with other vehicles or obstacles that can cause significant material and human damage.
In these conditions, manually following another aircraft at the correct speed and at the correct distance (with a safety distance to be observed) represents an additional workload for the pilot, and can prove difficult, even impossible, if the operational conditions are degraded (for example: reduced visibility, bad weather, wet or contaminated runway).
Moreover, even assuming the best case scenario where the pilot has an automatic taxiing function and only has to manually control the speed of the aircraft (the trajectory being followed laterally automatically), manual piloting leads to an under-use of the operational capabilities of the aircraft. In particular:                controlled manually, the speed of the aircraft is less than it could be if it were controlled automatically, because the pilot generally prefers to be prudent and be well in control of his speed. Consequently, the overall speed of the convoy is lower;        in terms of distance between aircraft within a convoy, the pilot, out of caution, gives himself wide safety margins, which could be calculated more accurately if automatically following the speed; and        in cases of poor visibility conditions, this convoy following maneuver is difficult (even impossible) and potentially hazardous in manual piloting mode.        
Finally, currently, there is no functional framework for ensuring the coherence of the convoy by the sharing of information between the aircraft and ground control, and between the aircraft themselves. There is also no formal operational procedure for managing convoys of aircraft, in particular the maneuvers of aircraft wanting to enter or leave the convoy. Consequently, ground control is obliged to manage each aircraft of the convoy individually, and cannot manage the convoy as a whole.